The spring helps relieve stress from impacts, a more comfortable, softer feel and will increase the lifespan of your hammock, in addition your mounting surface.Easy setup and take down of your favorite hammocks ChairsCan allows you to rotate the chair without tangling the ropesperfectfor Hanging Hammock Chairs and Porch Swings hammock chair, porch swing,yard sling swing.colour: silverMaterial: iron galvanizedsize: diameter 7mm; 10.8x 3.9 x 3.9cmPackage Contents: 2*Hammock SpringOnly the above package content, other products are not included.Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.